It is often necessary to monitor several electric signals relative to the maintenance (observance) of predetermined ranges of tolerances in cases of monitoring electric equipment such as, for example, communication or data processing equipment. It is true that the above-mentioned known circuit arrangements could be applied for this purpose. Nevertheless, relative and circumstantial functional steps would have to be programmed resulting in a complicated structure of the circuit. In the course of the successive comparison of an analog electric signal with the reference values, it is necessary to feed into a data register a reference value for each comparison process and to query a blocking register topped by a comparator. The results of the query (inquiry) of the blocking registers must be evaluated in a microprocessor only after the above steps. Erroneous monitoring results can occur during the relatively long period of time between when the analog signal changes and the queries of the blocking registers when the evaluating microprocessor is interrupted by other programs.
Especially for the above-mentioned purpose of application, it should be possible to execute automatically the monitoring of several analog signals in a cyclical sequence and to have the monitoring results available after each respective cycle. Even this is not easily realizable with the known circuit arrangement.